1. Field of the Invention
This invention relates to an optical atmospheric communication system, and more particularly is suitably applied to a case of transmitting the desired information via a optical beam propagating through the atmosphere.
2. Description of the Prior Art
In a conventional optical atmospheric communication apparatus, a device wherein a part of the optical beam to be outputted to the transmitting object is reflected and can be observed with an observation light to be received from the transmitting object has been proposed (Japanese Patent Applications No. 20916/1990 and No. 138120/1988).
According to this method, the projecting position of the optical beam can be confirmed depending on the optical beam reflected and position of transmitting object can be detected by observing with such as a telescope. The projecting position of the optical beam can be easily adjusted depending on the observation result.
Furthermore, after setting up the optical atmospheric communication apparatus receives the optical beam coming from the transmitting object by the position detecting sensor and thus detects the position of transmitting object.
Moreover, in the optical atmospheric communication apparatus, the reflected optical beam is received by the position detecting sensor and thus the projecting position of optical beam is detected.
With this arrangement, the projecting position of the optical beam is corrected in order that the position of the transmitting object coincides with the projecting position of the optical beam, and in the case where the optical atmospheric communication apparatus vibrates such as by wind, the optical beam can irradiate correctly the transmitting object (U.S. patent application Ser. No. 5,221,985).
Then, in this type of optical atmospheric communication apparatus, while the optical beam of transmitting object can be received, the projecting position of the optical beam can be corrected based on the optical beam.
Accordingly, in the optical atmospheric communication apparatus, while one side of the optical beam irradiates the other side of optical atmospheric communication apparatus, the projecting position of the optical beams can be corrected reciprocally and the information can be sent and received steadily.
However, in this type of optical atmospheric communication apparatus, if both beams discontinue irradiating the opposite transmitting objects, the position of the transmitting object can no longer be detected.
Therefore, in this type of optical atmospheric communication apparatus, there is a negative point wherein the projecting position of the optical beam cannot be corrected and, the projecting position adjusting work of the initial set up stage must be repeated.
Practically, the optical atmospheric communication apparatus vibrates for various reasons in the case where it is set up in the outdoors. There are occasions when the apparatus become incapable of irradiating the opposite transmitting objects with each other.
In this case, if the projecting position can be adjusted automatically, a complicated adjusting work can be omitted and thus the usability of this type of optical atmospheric communication apparatus can be improved.
Moreover, since the optical atmospheric communication apparatus can be set up in the places where the shocks are so severe that apparatuses are usually unable to irradiate the opposite transmitting objects frequently, the places for setting up the optical atmospheric communication apparatus can be expanded.